Lex Parsimoniae
by Harikari
Summary: When a series of suspicious and dangerous accidents start to happen at Hogwarts John, a seventh year Gryffindor determined to put a stop to it all, enlists the help of his loathed but brilliant classmate - Sherlock Holmes.
1. Prologue

**Title: **Lex Parsimoniae  
><strong>Author: <strong>Harikari  
><strong>Rating:<strong> PG-13  
><strong>Pairing:<strong> Sherlock/John  
><strong>Warnings:<strong> Violence, strong language, possible **major spoilers** for both seasons of Sherlock, sort of a crossover/fusion with the HP universe that takes place in that time after the End of the HP series but before the Epilogue (probably won't follow the HP history/facts/world exactly but there is some mention of it), not Brit-picked, etc.  
><strong>Disclaimer:<strong> Don't own em'. Written for fun, not profit.

**Summary:** When a series of suspicious and dangerous accidents start to happen at Hogwarts John, a seventh year Gryffindor determined to put a stop to it all, enlists the help of his loathed but brilliant classmate - Sherlock Holmes.

* * *

><p>John was sitting at the Gryffindor table, staring up at the Headmistress and wondering what sort of dinner would be served after her annual Beginning of Year speech was over. He was hungry, but he didn't particularly feel like eating ham or-<p>

In a flash of movement Molly elbowed him in the gut.

"Jesus," he hissed. "Ouch, Molly. What-"

The girl's arm shot out; she pointed firmly at the large, ornate doors that led out into the entrance hall. _"Look," _she insisted and then put her arm back down, folded both of her hands in her lap and started to sort of bounce in her seat a little. Like she was excited.

John turned and looked.

The doors had been flung open and a gaggle of very small looking first year students were making their way into the Great Hall, trailing after a rather harried looking Hagrid. But the Care of Magical Creatures instructor and the obviously nervous first years were not the reason a sudden chorus of hisses and harsh whispers had started up (a chorus the seventh year Gryffindor had managed to miss while pondering over the soon to come start of year feast).

No. The cause of the hushed chaos was the teenager walking at the head of the small group of first years, just behind Hagrid.

He was tall and pale and had dark hair and startling, bright eyes and looked about John's age - much too old to be a first year student at Hogwarts School of Witchcraft and Wizardry. And yet there the boy was, coming to a stop along with all of the eleven and twelve year olds in front of the long table where Headmistress McGonagall and the professors all sat.

"Here they are, ma'am," said Hagrid and waved his arm in a vague sort of way to take in the group of children behind him. "They're all yours." And with that the half giant moved around the table and to his own seat; as he settled into his large chair he kept his eyes on the teenager, as if nervous.

McGonagall nodded at the man in thanks and stood, swept her sharp gaze across all of the house tables. The hissing and whispers faded and she nodded again, sharply.

Silently and quickly she moved to place the familiar four-legged stool in front of the long table where the Professors were all looking on, sat the frayed and rather ugly looking Sorting Hat atop the stool and waited.

After a long moment of first years fidgeting where they stood and a number of older students shifting nervously in their seats the hat began to sing.

It was a normal sort of song for the hat, nothing that gave a clue as to who the pale, young stranger standing in the midst of the little first years was. Just clever rhymes about bravery and brains and heart and cunning.

The singing came to an abrupt stop; there was a scattering of half-hearted applause. Then, finally, McGonagall motioned to the young man. "Mr. Sherlock Holmes, our new transfer student, will go first. Then, as usual, I will call out of the names of our first years in alphabetical order."

That bit of information led to an immediate burst of conversation that almost just as immediately cut off when the Headmistress pursed her lips and glared around at the tables. "Mr. Holmes? If you would. Please have a seat." She gestured at the stool with her wand and stood waiting for Sherlock, who was staring up at the enchanted ceiling (it was a clear night, the stars shining brightly in the dark sky) to sit.

"That won't be necessary," said Sherlock. He was still looking up at the ceiling as he spoke.

McGonagall blinked. John noticed Hagrid sitting up a little straighter in his seat, leaning forward.

"I'm..." The Headmistress trailed off.

She shook her head as if to clear it and then started again. "Have a _seat_, Mr. Holmes. This is the Sorting Hat - it will tell you which House you belong in." She made a sort of shooing motion with her hands.

Sherlock's gaze left the ceiling, drifted to the (rather imposing, in John's opinion) woman standing in front of him. "I know what it is. I know why you want me to sit. It's not necessary."

McGonagall bristled. She looked annoyed, angry. "It certainly is necessary, Mr. Holmes. All students are required to be sorted-"

"Yes," Sherlock went on. "Of course. I know. But I also know exactly how that hat works, what it bases it's decisions on. I know that how much it, for lack of a better word, _thinks_ a person belongs in Hufflepuff or Slytherin does not matter. Because just asking it to be in a House or to not be in a House - just making a _choice _is enough to override the hat's...decision."

McGonagall was turning red. "Whether that assumption is true or not-"

"It is. And it's not an assumption."

"You still need to take a seat. The hat needs to be placed on your head."

"No. I just need to be within a certain proximity of the thing." He took a single step closer to the stool. "And I need to have made my choice." He turned to look around at all the gaping students, seemed to carefully study each table before he turned back to McGonagall. "And I have. Though none of the Houses look _particularly_ appealing."

"What in the bloody hell?" shouted Sally Donovan from her place at the Ravenclaw table. "What an absolute freak! Who do you think you are?"

The Headmistress - who looked as if she wanted to take points away from the transfer student in front of her but couldn't work out just how she could do that if he wasn't even in a _House_ yet- didn't even seem to hear the girl. "You must-"

"I choose Gryffindor," said Sherlock.

And a split second later the hat - as if it had been jolted with a burst of electricity - _jumped_.

"GRYFFINDOR!" it shouted before landing back on the stool and going still. Silent.

Without a word Sherlock Holmes walked away from the four-legged stool and the Headmistress, made his way over to the Gryffindor table. He took an empty seat next to a wide eyed second year.

There was a beat of complete quiet.

Then McGonagall cleared her throat; pulled a scroll from the depths of her robes and unrolled it. She cleared her throat again, loudly, and began to call out names.


	2. Part One

"I think he's nice," said Molly.

John swung his book bag onto his shoulder; frowned in confusion as he adjusted the strap. "What? Who?"

"Sherlock Holmes," replied the girl. "I like him."

_Oh_, thought John. _Him_.

The bloke who had managed to antagonize the entire school during the Start of Term Feast a few weeks before. Who had just finished explaining to their Muggle Studies professor and to the class at large why exactly the provided text and its statements on muggle law enforcement were complete rubbish.

Of _course _Molly Hooper, John's smart and well-meaning but sometimes oblivious best friend, liked Sherlock Holmes.

John didn't know what to say to that. He made a '_hmm_' sound in lieu of a reply.

She continued as they headed for the door. "I mean, he's really smart. Maybe even genius smart. I don't think he means to...come off the way he does."

She was silent for a moment before starting again. "I think he's _misunderstood_."

Except for the still red-faced and fuming professor, they were the last to leave the classroom. They emerged into the hallway in time to witness Anderson, a seventh year Ravenclaw, swerve sharply. He swerved right into Sherlock, bumped the pale teenager _hard_in the shoulder. The small stack of books the tall Gryffindor was holding went flying and Anderson barked a harsh laugh before disappearing around a corner.

Molly made a soft sound of distress and hurried over to Sherlock. Reluctantly, John followed.

"What a prat," declared the girl when they reached their housemate. She bent to pick up the almost comically huge Astronomy tome that had landed face down on the floor; made an attempt to dust it off a bit before handing it over to Sherlock.

John grabbed the more normal sized book next to Molly's left shoe, held it out so the other boy could take it.

Slowly, after adjusting his awkward hold on the retrieved Astronomy text, Sherlock pulled it from his grasp.

"Oh," he said and his bright eyes shifted from Molly to John and back again. "It's you two."

He moved to stuff both books into his bag.

Molly beamed. "Yes. I'm Molly and this is-"

"I know who you are," cut in Sherlock. "Molly Hooper and John Watson. Seventh years, Gryffindor House, not particularly liked or disliked by your classmates, can almost always be found with each other..."

In an instant he reached for John's hand, pulled it up to eye level for a moment before dropping it again. "But not due to a romantic attachment. Friends, close friends. You act almost like siblings so your families are probably close, too. You knew each other long before starting at Hogwarts."

He pursed his lips and reached out again, almost touched Molly's hair (which was up in a neat ponytail) before pulling his hand back. He looked the girl in the eye. "You're looking for romance but aren't having much luck so far."

Molly's wide smile and the faint blush that had arisen on her skin when Sherlock had reached for her hair faded a little at that.

Sherlock didn't seem to notice, hardly even paused. "John, left handed, slightly undersized for your age, you're what the average person would consider a smart boy and are doing well in your classes. But you're restless for some reason. Bored?" His eyebrows raised, as if in interest. "Maybe you-

Molly jumped in. "He has been restless," she said. "He hurt his shoulder playing Quidditch last year. It was the last game of the season and he got knocked off of his broom by this awful Slytherin." She shrugged and shook her head. "He used to love Quidditch and all, but he hasn't even been able to _fly _much since the accident. So...restless."

The tall teenager, his face unreadable, stared at the girl for a beat before nodding. He zipped up his bag.

"Wow," started John before the other Gryffindor could turn and walk away. "That was..."

"What?" asked Sherlock, a little sharply.

"Brilliant. Absolutely brilliant."

Sherlock didn't move for a moment. Then, "Huh. That's not what people normally say."

"What do people normally say?" asked John.

"Piss off."

John couldn't hold back an amused laugh; Sherlock eyed him up and down again, as if seeing him for the first time. (Which was obviously not the case, considering what he had been able to deduce about the former Quidditch player only moments before.)

Molly was, suddenly, practically vibrating in place beside them. "Right. Well. We're heading to the library to get some homework done before dinner."

John waited expectantly for his friend to speak again, to invite Sherlock along with them.

She didn't.

_Maybe she doesn't just think he's nice. Maybe she likes him a_ lot, he thought. _So much that just being around him is making her nervous..._

That made sense. Considering her reaction when she had first spotted the teenager during the Start of Term Feast, her nervous bouncing now, the way she had blushed moments before and the fact that this was their first proper conversation with their new housemate.

Without so much as a wave or a grunt or a belated thank you for their help, Sherlock turned away. He disappeared around the same corner Anderson had a few minutes earlier.

Next to him, Molly exhaled deeply.

"To the library, then?" asked John.

They started down the corridor.

* * *

><p>The common room was quiet. It was hours after dinner, nearly time for bed. A few second year Gryffindors were playing a game of Wizard's Chess in one corner and both Molly and John were sprawled on the squashy couch near the large fireplace.<p>

Molly appeared to be absorbed in an article in the Daily Prophet (something about Harry Potter, the amazing former Boy Wizard who had defeated Voldemort, denying the recent rumors that he was now aiming for a political career). John was half-heartedly perusing the encyclopedia of magical ailments that Madam Pomfrey had insisted he read when he had helped a sniffling first year with a hurt ankle to the infirmary earlier that week and had expressed an interest in healing.

Yawning, he closed the huge book with a _snap _and lifted his arms over his head in a stretch. He waited until Molly moved to turn the page to speak. "So you like Sherlock Holmes?" It was almost more of a statement than a question.

The girl looked up from the newspaper. "What?" She paused for a moment, expression blank, as her mind caught up with John's words. "Oh. Yes. Like I said, I think he's nice. Just-"

"Misunderstood," cut in John. "Right."

"Why?" asked Molly. "You don't like him?"

"It's not that." John shrugged and scooted so he was sitting on the edge of the sofa, his book in his lap. "I don't really know him well enough to say I dislike him. He's certainly...blunt. And smart. What he did yesterday, figuring out all of those things about us with just a close look? That was wicked."

His friend smiled a soft, slightly crooked smile. "Yeah," she said in what John thought sounded like a dreamy voice. "That was...something. Wasn't it?"

John nodded and stared into the unlit fireplace. Molly stared at him for a moment before neatly folding the Prophet up and placing it on the sofa arm (where she had liberated it from earlier that night).

"It's late. I better get to bed if I don't want to oversleep and be late for my first class tomorrow morning." She stood; hesitated when John didn't budge "Aren't you going to bed, too? Professor Longbottom is fair but if we-"

"Yeah," he said. "In a minute. G'night, Mol."

"Yeah. Goodnight, then." And with that the girl drifted up the stairs to the girl's dormitories.

Planning to put away the text on his lap, John reached for his book bag (thrown carelessly on the floor next to the sofa). He opened it; saw a few stray bits of unfamiliar paper among his scrolls and notebooks and texts and pulled them out. It was the mail his eagle owl, Ares, had delivered to him that morning. In his hurry to swallow down some breakfast and get to class on time he had forgotten all about it.

Quickly, he looked through it. Two of the three pieces of mail were simple flyers. One was for the candy shop in Hogsmeade and the other - more unofficial looking -promised useful advice and help with _relationships, homework and more _to Hogwarts students. Some sort of advice column or tutoring gig, then.

The candy shop advertisement had a few coupons so John folded the flyers and stuffed them back into his bag.

The last piece of mail was in an envelope. A small, blank envelope. John opened it up, pulled out the folded bit of paper inside. The short letter, written in black ink, read:

_Meet me in the entrance hall at 10. -SH_


End file.
